Intermodal cargo containers (also referred to as freight or shipping containers) are reusable transport and storage units for moving products and raw materials between locations, including between countries. Intermodal cargo containers are standardized to facilitate intermodal transport such as among marine transport, freight train transport, and freight truck transport. Standardization of cargo containers also is referred to as containerization.
Containerization has provided global commerce with many benefits. Shipped goods move more easily and cheaply. Manufacturers know that goods loaded at one location can be readily unloaded at the destination. Cargo security has been improved, as containers are usually sealed and can be locked to discourage tampering and theft. Containers also have a longer service life, and there is a stronger market for used containers. Additionally, the costs of cargo containers themselves is lowered because a manufacturer can make these in larger volume knowing that potential customers are available all over the world.
Several international standards have been created to promote international containerization. For instance, the International Organization for Standardization (ISO) has promulgated applicable standards including R-668 to define terminology, dimensions, and ratings; R-790 to define identification markings; R-1161 to recommend corner fittings; and R-1897 to set forth dimensions for general purpose containers. Other standards include ASTM D5728-00, ISO 9897 (1997); ISO 14829 (2002); ISO 17363 (2007); ISO/PAS 17712 (2006); ISO 18185 (2007); and ISO/TS 10891 (2009). An international specification for coating/paint performance is provided by IICL (Institute of International Container Lessors). See also International Organization for Standardization (ISO), Freight Containers, Vol. 34 of ISO Standards Handbook, 4th Ed., 2006, ISBN 92-67-10426-8; and Levinson, Marc, The Box: How the Shipping Container Made the World Smaller and the World Economy Bigger, Princeton, N.J., Princeton University Press, 2006, ISBN 0691123241. Each of these standards and publications is incorporated herein in its entirety for all purposes.
Cargo containers experience harsh, corrosive environments during their service life. When shipped by sea, the containers are exposed to the corrosive effects of salt water. When exposed to nature, the containers must withstand wind, sun, hail, rain, sand, heat, and the like. Containers exposed to the sun can bake to temperatures of 82° C. (180° F.) or even higher.
Accordingly, cargo containers must be made in a way that allows the containers to survive this exposure for a reasonable service life. As one strategy, containers can be made from corrosion resistant materials such as stainless steel, weathering steel (also known as weather steel, COR-TEN brand steel, or CORTEN brand steel). For example, a refrigerated cargo container is a type of intermodal cargo container used in intermodal freight transport that is refrigerated for the transportation of temperature-sensitive cargo. A typical refrigerated cargo container includes a steel frame and steel wall panels welded to the frame. In one embodiment, the frame of a refrigerated cargo container may be made from weathering steel, while the wall panels are made from a stainless steel such as muffler grade stainless steel. The frame often is protected against corrosion such as by galvanizing the frame or coating the frame with a Zn-containing primer. The frame is then further protected with a waterproof barrier. Often, a two-part epoxy coating is used to coat the frame. The epoxy coating is then topcoated as uncoated epoxy tends to degrade in sunlight. The stainless steel wall panels are sufficiently corrosion-resistant that it is not strictly necessary to apply protective coatings to the stainless steel. It nonetheless often is desirable to apply a coating to the stainless steel in order to provide decoration, trademark indicia, bar code information, and other indicia.
Historically, mostly solvent-based coating systems have been used to protect cargo containers as many proposed water-based systems have been unable to satisfy the applicable performance demands and/or standards. It has been very difficult to formulate water-based coating systems that show acceptable adhesion when applied directly to stainless steel. Water-based coatings also tend to have greater problems with respect to sagging, leveling, cratering, and cracking. Consequently, only solvent-based coating systems have found widespread commercial acceptance in the industry. The container industry retains a strong bias against using water-based coating systems.
With increased environmental awareness, there is a strong desire to develop improved technology that would allow use of water-based coating systems to protect cargo containers or other substrates. The industry strongly desires a commercially available, water-based coating system that is able to satisfy the stringent demands of the intermodal cargo container industry, particularly when used to coat stainless steel substrates.